The cessation of reproductive function is one of the most dramatic and fairly rapid endocrine changes in the life of a female and carries profound and broad repercussions. At one time, it was thought that decreasing estradiol concentration, resulting from exhaustion of ovarian follicles, caused the menopause. Now, it is clear that many factors interact to bring about declining reproductive function and the cessation of reproductive cycles. Furthermore, we are beginning to appreciate the most- reproductive state affects multiple functions that extend beyond the traditional reproductive axis. An increasing number and an increasing proportion of women will liver a larger fraction of their lives in the postmenopausal state. Therefore, it is critical that we deepened our understanding of the factors that regulate the transition to acyclicity and, conversely, the impact of transition to acyclicity on the function of multiple systems. The program is organized into five research projects that are supported by one Core. The projects are integrated and coordinated to test the following hypotheses (1) changing estrogen responsiveness governs the health and function of ovarian follicles during aging, (2) age-related and estradiol-dependent alterations in the pattern of expression in the ovarian metalloproteinases and their inhibitors result in abnormalities in follicular development and ovulation, (3) aging and/or the cumulative exposure to estradiol regulate changes in somatotroph and lactotroph function, (4) alterations in glutamatergic and adrenergic regulation of GnRH neurons cause changes in their ability to induce LH surges; and (5) estradiol plays a critical protective role in the brain; therefore, declining estradiol concentrations lead to an increased vulnerability to brain injury and neurodegeneration. An Administrative/Animal ore supports all of the projects, providing organizational planning, integrating results from each project into a more comprehensive overview, and maintaining all animal records and coordinating their optical endocrine treatments and use. We submit this program project proposal because we share interests in interdependent aspects of reproductive aging. A common threat that weaves through all of the projects is our interests in the role of estradiol in aging. Finally, this mechanism of support will permit us to use aging animals in the most optimal manner, allowing us to compare data and economize on the costs of aging animals.